Design and Synthesis of Imidazolium-Mediated Tröger’s Base-Containing Ionene Polymers for Advanced CO2 Separation Membranes
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Abstract
It is highly desirable to integrate the CO_2 solubility benefits of ionic liquids (ILs) in polymeric membrane systems for effective CO_2 separations. Herein, we are exclusively exploring a series of four novel imidazolium-mediated Tröger’s base (TB)-containing ionene polymers for enhanced CO_2 separation. The two diimidazole-functionalized Tröger’s base monomers synthesized from “ortho”- and “para”-substituted imidazole anilines were polymerized with equimolar amounts of two different aromatic and aliphatic comonomers (α,α´ -dichloro-p-xylene and 1,10-dibromodecane, respectively) via Menshutkin reactions to obtain four respective ionene polymers (I'm-TB (o&p)-Xy] [Cl] and ([Im-TB(o&p)-C_10] [Br], respectively). The resulting ionene polymers having halide anions were exchanged with [Tf_2N]¯ anions, yielding a novel Tröger’s base material [Im-TB(x)-R] [Tf_2N] or “Im-TB-Ionenes”. The structural and physical properties as well as the gas separation behaviors of the copolymers of aromatic and aliphatic Im-TB-Ionenes have been extensively investigated with respect to the regiochemistry of imidazolium groups at the ortho and para positions of the TB unit. The imidazolium-mediated TB-Ionenes showed high CO_2 solubility and hence an excellent CO_2/CH_2 permselectivity of 82.5. The Im-TBIonenes also displayed good thermal and mechanical stabilities.